Biomolecules Question 179
Question: When $ \alpha $ -D-glucose and $ \beta $ -D-glucose are dissolved in water in two separate beakers I and II respectively and allowed to stand, then -
Options:
A) specific rotation in beaker I will decrease while in II will increase upto a constant value
B) the specific rotation of equilibrium mixture in two beakers will be different
C) the equilibrium mixture in both beakers will be leavorotatory
D) the equilibrium mixture in both beakers will contain only cyclic form of glucose
Show Answer
Answer:
Correct Answer: A
Solution:
[a] $ \alpha $ -D-glucose or $ \beta $ -D-glucose when dissolved in water and allowed to stand, following equilibrium is established.
$ \underset{( +111{}^\circ )}{\mathop{\alpha -D-glucose}}\rightarrow ~Openchainform $
$ \rightarrow \underset{(+19{}^\circ )}{\mathop{\beta -D-glucose}} $
Specific rotation of $ \alpha $ -form falls, while that of $ \beta $ -form increases until a constant, value of $ +52.5{}^\circ $ is reached at equilibrium. This phenomenon is known as mutarotation.
BETA
